U.S. Pat. No. 4,818,275 (Theodoridis) discloses the utility of N-[2,4-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4- triazol-1-yl]phenyl]methanesulfonamide (sulfentrazone, I) as a herbicide. ##STR1##
U.S. Pat. No. 4,818,275 discloses the preparation of I by treatment of the corresponding aryl amine II with methanesulfonyl chloride and triethylamine in methylene chloride, to give the bis(methanesulfonyl)amino derivative III, followed by treatment with sodium hydroxide in aqueous ethanol to give I. This procedure employs 2.25 molar equivalents each of methanesulfonyl chloride and triethylamine. The apparent overall yield is about 66%.
In Synthesis and Chemistry of Agrochemicals III, American Chemical Society; Washington D.C., (1992); pages 136 and 137, Theodoridis et al disclose that compound I can be prepared directly from aryl amine II by treatment of II with methanesulfonyl chloride and pyridine in methylene chloride at room temperature. No details regarding the relative amounts of starting materials and reagents, the reaction time, or the yield are provided. ##STR2##
Conventional processes for the preparation of secondary methane sulfonanilides directly from primary aryl amines and methanesulfonyl chloride require the use of a molar equivalent or more, relative to the methanesulfonyl chloride, of a hydrochloric acid scavenger. This can be accomplished by using a twofold excess of the primary aryl amine or by using an amine base such as pyridine or triethylamine. In the Journal of the American Chemical Soc. (1929), 51, 1272-1274, Marvel et al describe the reaction of methanesulfonyl chloride with two molar equivalents of aryl amines to produce methanesulfonanilides. In the Journal of the American Chemical Soc. 1992, 114, 1743-1749, King et al report the preparation of methanesulfonanilide from aniline using 1 molar equivalent of methanesulfonyl chloride and 1 molar equivalent triethylamine. In Journal of Organic Chemistry, (1987), 52, 4377-4379, Lis and Marisca report the preparation of methanesulfonanilides using 1.1 molar equivalents each of methanesulfonyl chloride and pyridine relative to the primary aryl amine. In scaling up these processes, the hydrochloric acid scavenger must be recovered and reused or disposed of as part of the process waste streams. Recovery of the acid scavenger results in added processing costs while disposal results in increased waste treatment costs.
In the preparation of methanesulfonanilides from primary aryl amines, it is often difficult to drive the conversion of the primary aryl amine to completion without the formation of a substantial quantity of the corresponding bis(methanesulfonyl)amino derivative. In order to optimize the conversion of a primary aryl amine to a secondary sulfonamide, it is often necessary to stop the reaction when only partial conversion of the aryl amine has been achieved. This leads to reduced yields which can only be compensated for by additional processing to recover aryl amine. Alternatively, as shown by Theodoridis in U.S. Pat. No. 4,818,275, the reaction can be driven to completion and the co-product bis(methanesulfonyl)amino derivative converted back to the secondary sulfonamide. This necessitates the use of larger amounts of methanesulfonyl chloride and acid scavenger and further increases costs.
The process of the present invention avoids the problems of the prior art by providing a catalytic process which does not require the use of a molar equivalent or more of an amine base and allows for the high conversion of aryl amine II to methanesulfonamide I without the formation of substantial quantities of bis(methanesulfonyl)amino III.